The Trace Event Profiling Tool (about:tracing)

When diagnosing performance problems it can be valuable to see what Chrome is doing "under the hood." One way to get a more detailed view into what's going on is to use the about:tracing tool.

Tracing records activity in Chrome's processes (see multi-process architecture for more on what each process is doing). It records C++ or javascript method signatures in a hierarchical view for each thread in each process. This is a lot of information, but sifting through it can help identify performance bottlenecks, slow operations, and events with irregular lengths (leading to e.g. framerate variation).

Jank Case Study 1; then read this, for further examples of how to effectively use about:tracing in conjunction with the Dev Tools timeline

Note that to understand what's happening in trace events you'll need a basic understanding of how the browser works. The above articles provide enough to get started, but it's recommended to first read at minimum: